Influence of potential on the friction and wear of mild steel in a model aqueous lubricant

An electrochemical cell has been designed, based on a Cameron-Plint friction machine, which enables measurement of friction and wear under conditions of controlled potential. For mild steel in a pH 9 aqueous solution of sodium octanoate, varying the potential of the steel over the range --1 to +1 V vs. SHE produced three distinct friction-wear regimes: high friction/low wear, low friction/high wear, and low friction/low wear. These regimes were ascribed to potential dependent changes in the coverage and stability of a lubricating octanoate film on the surface of the steel. Increasing the contact stress amplified the effect of potential on wear, and confirmed that the surface film retained its lubricity at contact stresses capable of causing plastic deformation of the steel.